Optical fluid analyzer sampling tool using open beam optical construction

ABSTRACT

An apparatus for estimating a property of a fluid of interest downhole includes: a carrier configured to be conveyed through a borehole penetrating an earth formation; an emitter disposed at the carrier and configured to emit electromagnetic energy; and a sample chamber configured to contain a sample of the fluid of interest and having a window transmissive to electromagnetic energy emitted by the emitter, the electromagnetic energy interacting with the sample of the fluid of interest with a characteristic related to the property; wherein a path of the emitted electromagnetic energy from the emitter to the window of the sample chamber traverses a gas or a vacuum.

BACKGROUND

Earth formations are used for various applications such as hydrocarbon production, geothermal production, and carbon dioxide sequestration. In order to characterize formations of interest, various types of downhole tools are conveyed through boreholes penetrating the formations and used to take different types of measurements.

One type of downhole tool is a fluid analysis and sampling tool, which includes an optical fluid analyzer. In the optical fluid analyzer sampling tool, a sample of a fluid of interest is extracted and placed in a sample chamber. Then, a spectrum of light either transmitted through or reflected from the fluid of interest is measured and correlated to a property of the fluid of interest, such as chemical composition. Typically, measurements are performed every few seconds with a continuous flow of fluid through the sample chamber. It would be well received in the drilling industry if the optical fluid analyzer sampling tool could be improved to increase the accuracy and precision of measurements.

BRIEF SUMMARY

Disclosed is an apparatus for estimating a property of a fluid of interest downhole. The apparatus includes a carrier configured to be conveyed through a borehole penetrating an earth formation; an emitter disposed at the carrier and configured to emit electromagnetic energy; and a sample chamber configured to contain a sample of the fluid of interest and having a window transmissive to electromagnetic energy emitted by the emitter, the electromagnetic energy interacting with the sample of the fluid of interest with a characteristic related to the property; wherein a path of the emitted electromagnetic energy from the emitter to the window of the sample chamber traverses a gas or a vacuum.

Also disclosed is an apparatus for estimating a property of a fluid of interest downhole. The apparatus includes: a carrier configured to be conveyed through a borehole penetrating an earth formation; an emitter disposed at the carrier and configured to emit electromagnetic energy; a sample chamber configured to contain a sample of the fluid of interest and comprising a window transmissive to electromagnetic energy emitted by the emitter, the electromagnetic energy interacting with the sample of the fluid of interest with a characteristic related to the property; and an analyzer configured to receive and analyze electromagnetic energy that interacted with the fluid of interest to estimate the property; wherein a path of the emitted electromagnetic energy from the emitter to the window and another path from the window to the analyzer traverses a gas or a vacuum.

Further disclosed is a method for estimating a property of a fluid of interest downhole. The method includes: conveying a carrier though a borehole penetrating an earth formation; containing a sample of the fluid of interest in a sample chamber comprising a window transmissive to electromagnetic energy; and emitting electromagnetic energy from an emitter disposed at the carrier to the at least one window along a path that traverses a gas or a vacuum; wherein the emitted electromagnetic energy traverses the at least one window and interacts with the sample with a characteristic related to the property.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 illustrates an exemplary embodiment of an optical fluid analyzer sampling tool disposed in a borehole penetrating the earth;

FIG. 2 depicts aspects of an open-beam optical path used in the optical fluid analyzer sampling tool;

FIG. 3 depicts aspects of an optical axis of sapphire windows in a sample chamber used for transmissive spectroscopy;

FIG. 4 depicts aspects of an optical axis of a sapphire window in a sample chamber used for reflective spectroscopy; and

FIG. 5 illustrates a flow chart of a method for estimating a property of a material of interest downhole.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method presented herein by way of exemplification and not limitation with reference to the Figures.

FIG. 1 illustrates a cross-sectional view of an exemplary embodiment of a system to estimate a property of a downhole fluid of interest. A bottomhole assembly (BHA) 11 is disposed in a borehole 2 penetrating the earth 3, which includes an earth formation 4. The BHA 11 includes an optical fluid sample analyzer 10 (i.e. downhole tool 10) configured to perform one or more types of measurements on a downhole fluid of interest, which may be disposed in the formation 4 or the borehole 2.

The BHA 11 is conveyed through the borehole 2 by a carrier 5. In the embodiment of FIG. 1, the carrier 5 is a drill string 6 in an embodiment known as logging-while-drilling (LWD). In an alternative embodiment, the carrier 5 can be an armored wireline in an embodiment known as wireline logging. Disposed at a distal end of the drill string 6 is a drill bit 7. A drilling rig 8 is configured to conduct drilling operations such as rotating the drill string 6 and thus the drill bit 7 in order to drill the borehole 2. In addition, the drilling rig 8 is configured to pump drilling fluid through the drill string 6 in order to lubricate the drill bit 7 and flush cuttings from the borehole 2. Downhole electronics 9 may be configured to operate or control the downhole tool 10, process data obtained by the downhole tool 10, or provide an interface with telemetry for communicating with a computer processing system 12 disposed at the surface of the earth 3. Operating, controlling or processing operations may be performed by the downhole electronics 9, the computer processing system 12, or a combination of the two. Telemetry is configured to convey information or commands between the downhole tool 10 and the computer processing system 12.

In one or more non-limiting embodiments, the downhole tool 10 performs reflective or transmissive spectroscopy measurements to determine a property, such as chemical composition, of a sample of the downhole fluid of interest. To obtain the sample, the downhole tool 10 includes a formation tester 13 configured to extract a sample of the downhole fluid of interest from the formation 4 and dispose the sample in a sample chamber 15. The sample chamber 15 may be configured to contain a static sample or to contain a continuous flow of sample fluid through the sample chamber 15, which may also be referred to as a probe cell or fluid cell. In one or more non-limiting embodiments, the formation tester 13 includes a probe 14 configured to extend from the tester 13 and seal to a wall of the borehole 2. The formation tester 13 reduces pressure within the probe 14 causing formation fluid to flow into the probe 14 from which the fluid can be disposed in the sample chamber 15. Spectroscopy measurements are performed on the sample while the sample is contained in sample chamber or while the fluid is continuously pumped through the fluid cell.

To perform the spectroscopy measurements, the downhole tool 10 includes an emitter 19 configured to generate and emit electromagnetic (EM) energy (e.g. light or photons). The emitted EM energy enters the sample chamber 15 through a window, transmissive to the EM energy, where the EM energy interacts with the atoms or molecules of the fluid sample. The EM energy resulting from the interaction has a characteristic related to the chemical composition of the fluid sample. In general, the characteristic is an amplitude or peak of received EM energy at one or more wavelengths or frequencies. An analyzer 16 is configured to receive the EM energy resulting from interactions with the fluid sample and to measure the amplitude of the received EM energy as a function of wavelength or frequency of the received EM energy. Hence, the analyzer 16 can determine the characteristic amplitude peaks at one or more wavelengths or frequencies and relate this information to a chemical composition. In one or more embodiments, the analyzer 19 is a grating spectrometer.

It can be appreciated that providing strong optical signals used to characterize the fluid sample can result in a higher signal to noise ratio than if weaker optical signals were used. In order to maximize the strength of optical signals used to characterize the fluid sample, the downhole tool 10 includes an open-beam optical path. The term “open-beam optical path” relates to at least a portion of an optical path that traverses a gas or a vacuum and excludes traversing an optical fiber in that portion of the path. In one or more embodiments, open-beam optical paths completely exclude an optical path traversing an optical fiber in order to achieve the highest optical signal intensity possible with the emitter 9.

In reflective spectroscopy, the light emitted by the emitter 9 follows an open-beam optical path and enters a window of the sample chamber 15. The light reflected by interactions with the fluid sample traverses the same window, follows an open-beam optical path and is received and analyzed by the analyzer 16.

In transmissive spectroscopy with reference to FIG. 1, the light emitted by the emitter 9 follows an open-beam optical path and enters a first window of the sample chamber 15 (on left side). Light due to interactions with the fluid sample that continues through the fluid sample exits the sample chamber 15 at a second window (on right side). From the second window, the light follows an open-beam optical path and enters the analyzer 16 where the received light is analyzed.

FIG. 2 illustrates a cross-sectional view depicting aspects of using open-beam optical paths for transmissive spectroscopy. One open-beam optical path is used to optically couple the light emitted by the emitter 19 to a first window 21 of the sample chamber 15. Light interacting with the sample and transmitted through the sample exits the sample chamber 15 by way of a second window 22. The light exiting the second window 22 is optically coupled to the analyzer 16 by another open-beam optical path. In one or more embodiments, the windows 21 and 22 are plates having two parallel surfaces and the light entering or exiting the windows 21 and 22 is perpendicular to the surfaces. In one or more embodiments, the emitter 19 may be an incandescent light bulb or light emitting diode (LED) and part of an emitter assembly that includes a reflector 20. The reflector 20 is configured to reflect, focus or concentrate emitted light on to the first window 21 in order to minimize or eliminate light leakage or loss and maximize the optical signal provided to the sample or to the analyzer 16. A lens 23 may also be used to focus or concentrate the emitted light to minimize or eliminate light leakage. The lens 23 may be part of the emitter assembly or be disposed external to the assembly in the open-beam optical path. In one or more embodiments, the emitter is a bulb with a tungsten filament. An advantage of the tungsten filament is that it emits light at a temperature much higher than the temperatures generally experienced downhole and, thus, the emitted light will not be affected by the high downhole temperatures. In one or more embodiments, the windows 21 and 22 are made of a crystal such as sapphire or diamond for example. These crystals are strong and can withstand the high downhole temperatures and pressures.

The open-beam optical paths illustrated in FIG. 2 traverse a gas, such as air or nitrogen for example, or a vacuum. In one or more embodiments, a housing 24 is configured to contain the gas or provide the vacuum. The housing 24 may also be used to support the lens 23 or optical components in the open-beam paths. In general, few if any optical components are used in the open-beam paths in order to minimize or eliminate optical signal loss due to the optical components. In one or more embodiments, no optical components are used in the open-beam paths.

FIG. 3 illustrates a cross-sectional view of an embodiment depicting aspects of transmissive spectroscopy where the emitted light and the received light for analysis are non-perpendicular (i.e., non-normal) to the windows 21 and 22. In the embodiment of FIG. 3, the windows 21 and 22 are formed as sapphire crystal plates with the optical axis or c-axis of the crystal being perpendicular to the planes of the plates. In this embodiment, the refractive index of the sapphire is independent of the incident angle of the light. Thus, the tool 10 may be configured so that the incident light or received light is non-perpendicular to the windows 21 and 22. FIG. 4 illustrates an embodiment depicting aspects of reflective spectroscopy similar to the embodiment of FIG. 3. It can be appreciated that the embodiments of FIGS. 3 and 4 depicting non-perpendicular directions of emitted and received light with respect to the sample chamber window or windows allows the optical fluid sample analyzer 10 to be built in a compact form where space in a downhole tool may be limited due the space limitations in a borehole.

FIG. 5 illustrates a flow chart for a method 50 for estimating a property of a fluid of interest downhole. Block 51 calls for conveying a carrier though a borehole penetrating an earth formation. Block 52 calls for containing a sample of the fluid of interest in a sample chamber comprising a window transmissive to electromagnetic energy. Block 53 calls for emitting electromagnetic energy from an emitter disposed at the carrier to the at least one window along a path that traverses a gas or a vacuum wherein the emitted electromagnetic energy traverses the at least one window and interacts with the sample with a characteristic related to the property. The method 50 may also include receiving electromagnetic energy that interacted with the sample using an analyzer such as a spectrometer. The method 50 may also include the electromagnetic energy emitted by the emitter or received by the analyzer traversing the window at a non-perpendicular (i.e., non-normal) angle with respect to a plane of the window.

It can be appreciated that the optical fluid sample analyzer 10 provides several advantages over traditional optical fluid analyzers. Traditional optical fluid analyzers use optical fibers to transmit light from a light source to a sample chamber for interaction with a sample and for receiving light at a spectrometer due to the interaction. However, light losses occur at each coupling or interface with the optical fiber such as between the light source and the optical fiber and between the optical fiber and a window in the sample chamber or probe cell for example. Similar light losses occur with the received light at optical fiber interfaces and couplings. These light losses result in decreased intensity of light available for interrogating the sample. A light wavelength resolution in the range of a few nanometers is required to distinguish hydrocarbon groups and lower intensity light may result in a lower signal to noise ratio, lower resolution, and a wavelength range that may affect measurements to distinguish hydrocarbon groups. Further, the open-beam optical path lends itself to providing a more compact configuration that conforms to the space limitations in downhole tools. The compact configuration allows the distance between sapphire windows in the sample chamber or probe cell to be increased to reduce the risk of clogging the chamber or cell by solids contained in the downhole fluid. Another advantage of greater distance between the windows is that light absorption by a thin layer of contamination on the windows is reduced in relation to the light absorption in the fluid of interest. Further, the open-beam configuration is more robust than an optical fiber to the downhole drilling environment as the optical fiber may get damaged with time due to severe vibrations during drilling.

In support of the teachings herein, various analysis components may be used, including a digital and/or an analog system. For example, the downhole electronics 9, the surface computer processing 12, the emitter 19 or the analyzer 16 may include the digital and/or analog system. The system may have components such as a processor, storage media, memory, input, output, communications link (wired, wireless, pulsed mud, optical or other), user interfaces, software programs, signal processors (digital or analog) and other such components (such as resistors, capacitors, inductors and others) to provide for operation and analyses of the apparatus and methods disclosed herein in any of several manners well-appreciated in the art. It is considered that these teachings may be, but need not be, implemented in conjunction with a set of computer executable instructions stored on a computer readable medium, including memory (ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), or any other type that when executed causes a computer to implement the method of the present invention. These instructions may provide for equipment operation, control, data collection and analysis and other functions deemed relevant by a system designer, owner, user or other such personnel, in addition to the functions described in this disclosure.

Further, various other components may be included and called upon for providing for aspects of the teachings herein. For example, a power supply (e.g., at least one of a generator, a remote supply and a battery), cooling component, heating component, magnet, electromagnet, sensor, electrode, transmitter, receiver, transceiver, antenna, controller, optical unit, electrical unit or electromechanical unit may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure.

The term “carrier” as used herein means any device, device component, combination of devices, media and/or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and/or member. Other exemplary non-limiting carriers include drill strings of the coiled tube type, of the jointed pipe type and any combination or portion thereof. Other carrier examples include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, bottom-hole-assemblies, drill string inserts, modules, internal housings and substrate portions thereof.

Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The terms “first” and “second” are used to distinguish elements and are not used to denote a particular order. The term “couple” relates to coupling a first component to a second component either directly or indirectly through an intermediate component.

It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.

While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

What is claimed is:
 1. An apparatus for estimating a property of a fluid of interest downhole, the apparatus comprising: a carrier configured to be conveyed through a borehole penetrating an earth formation; an emitter disposed at the carrier and configured to emit electromagnetic energy; and a sample chamber configured to contain a sample of the fluid of interest and comprising a window transmissive to electromagnetic energy emitted by the emitter, the electromagnetic energy interacting with the sample of the fluid of interest with a characteristic related to the property; wherein a path of the emitted electromagnetic energy from the emitter to the window of the sample chamber traverses a gas or a vacuum.
 2. The apparatus according to claim 1, wherein the optical path does not traverse an optical fiber.
 3. The apparatus according to claim 1, wherein the optical path traverses one or more optical elements configured to focus the emitted electromagnetic energy.
 4. The apparatus according to claim 1, further comprising a housing configured to contain the gas or provide the vacuum.
 5. The apparatus according to claim 4, wherein the housing is further configured to support one or more optical elements configured to focus the emitted electromagnetic energy.
 6. The apparatus according to claim 1, further comprising an analyzer configured to analyze electromagnetic energy that interacted with the fluid of interest to estimate the property, the electromagnetic energy that interacted with the fluid of interest traversing the window and following a path that traverses a gas or a vacuum.
 7. The apparatus according to claim 6, wherein the analyzer comprises a grating spectrometer.
 8. The apparatus according to claim 1, wherein the window comprises a crystal.
 9. The apparatus according to claim 8, wherein the window is a plate window having two parallel planes.
 10. The apparatus according to claim 9, wherein an optical axis of the plate window is perpendicular to the planes.
 11. The apparatus according to claim 10, wherein the emitted electromagnetic energy enters the window at an angle greater than zero with respect to the optical axis.
 12. The apparatus according to claim 7, wherein the crystal comprises a sapphire crystal or a diamond crystal.
 13. The apparatus according to claim 1, wherein the carrier comprises a wireline, a slickline, a drill string, or coiled tubing.
 14. An apparatus for estimating a property of a fluid of interest downhole, the apparatus comprising: a carrier configured to be conveyed through a borehole penetrating an earth formation; an emitter disposed at the carrier and configured to emit electromagnetic energy; a sample chamber configured to contain a sample of the fluid of interest and comprising a window transmissive to electromagnetic energy emitted by the emitter, the electromagnetic energy interacting with the sample of the fluid of interest with a characteristic related to the property; and an analyzer configured to receive and analyze electromagnetic energy that interacted with the fluid of interest to estimate the property; wherein a path of the emitted electromagnetic energy from the emitter to the window and another path from the window to the analyzer traverses a gas or a vacuum.
 15. The apparatus according to claim 14, wherein the electromagnetic energy emitted by the emitter and the electromagnetic energy received by the analyzer traverses the same window.
 16. The apparatus according to claim 15, wherein the analyzer is configured to perform reflective spectroscopy.
 17. The apparatus according to claim 14, wherein the window comprises a first window configured to pass the electromagnetic energy emitted by the emitter and a second window configured to pass the electromagnetic energy received by the analyzer.
 18. The apparatus according to claim 14, wherein the analyzer is configured for transmissive spectroscopy.
 19. A method for estimating a property of a fluid of interest downhole, the method comprising: conveying a carrier though a borehole penetrating an earth formation; containing a sample of the fluid of interest in a sample chamber comprising a window transmissive to electromagnetic energy; and emitting electromagnetic energy from an emitter disposed at the carrier to the at least one window along a path that traverses a gas or a vacuum; wherein the emitted electromagnetic energy traverses the at least one window and interacts with the sample with a characteristic related to the property.
 20. The method according to claim 17, further comprising receiving electromagnetic energy that interacted with the sample using an analyzer configured analyze the received electromagnetic energy to correlate the characteristic to the property.
 21. The method according to claim 17, wherein the window comprises a crystal plate having two parallel planes with an optical axis perpendicular to the planes and the emitted electromagnetic energy enters the window at an angle greater than zero with respect to the optical axis. 